The present application is directed to systems and methods for reworking composite materials.
Composites are used in a variety of applications in the aerospace industry, in space craft, and in other military and commercial applications. Increasingly, high temperature composites, such as Bismaleimide (BMI) resin composites are used in many of these applications. In certain applications, the composites must be capable of withstanding extreme conditions, including high temperatures of, for example, 300° F. to 500° F., and high humidity conditions, for long periods of time.
Parts made from composites may develop inconsistencies during use and require rework. The inconsistency may be sustained in any number of ways, such as by taking a hit during combat or other events or during severe weather conditions, or by exposure to high temperatures. It is desirable that any rework made to the composite be capable of withstanding the extreme conditions the original composite structure was designed to handle. In certain situations, it is also desirable that the rework conform to the original shape of the composite, so that the rework does not interfere with, for example, the aerodynamic design of the aircraft. Achieving conforming reworks can be difficult, given the complex shapes and highly curved surfaces of composite parts.
A number of processes have been used in the past for reworking composite parts. For example, bolted metal patches have been used for reworking aircraft composites. In these processes, a metal, such as titanium, is machined to form a patch having the desired shape and then bolted over the inconsistent portion of the aircraft. However, procuring titanium may require a long lead-time, and machining, forming and drilling titanium can be challenging. In addition, metal patches may increase the radar signature of the aircraft, and thus may not be a viable rework option for some aircraft.
Bonded, precured BMI composite patches have been used to rework BMI composite parts. In some processes, a BMI composite patch is formed from prepreg materials. The composite patch can then be cured on-aircraft using a release film which allows the patch to be removed from the aircraft after the cure step is complete, followed by a post cure in, for example, an autoclave or oven. After the post-cure is complete, the composite patch is bonded to the aircraft with a film adhesive. Bonding precured BMI composite patches in this manner can be a relatively long and complex process. In addition, the prepreg materials used to form the composite patch often have a limited shelf/storage life. Since prepreg materials generally require freezer storage, there are associated increased storage and transport related logistical costs. The limited shelf life, as well as the storage and transport related logistics, may be particularly problematic in certain military applications, where freezer storage may be limited, or where it may be desirable to rework an aircraft in the field so that it may be redeployed in a short amount of time.